C3.3 Energy Calculations

Question 1

Explain how a catalyst increases the rate of the reaction. [2]

Answer 1

• provides an alternative route

- with a lower activation energy

Question 2

Temperature before heating

20.7 °C

Temperature after heating

35.1 °C

Calculate the energy used to heat 50ml of water.
Use the equation Q = m × c × ΔT
The specific heat capacity of water = 4.2 J / g / °C [3]

Answer 2

35.1 - 20.7 = 14.4 [1]

q = 50 x 4.2 x 14.4 = 3024[1] J [1]

Question 3

Mass of spirit burner before ethanol was burned

72.80 g

Mass of spirit burner after ethanol was burned

72.10 g

Calculate the number of moles of ethanol (C₂H₅OH) that were burned.
Relative atomic masses (Ar): H = 1; C = 12; O = 16

Answer 3

72.80 - 72.10 = 0.7g [1]

12+12+1+1+1+1+1+1+16=46[1]

0.7/46 = 0.015[1]

Question 4

Explain why the incomplete combustion of methane is dangerous. [2]

Answer 4

Produces carbon monoxide (CO)[1]

Which is poisonous [1]

Question 5

Explain why, in terms of the energy involved in bond breaking and bond making, the combustion of methane is exothermic. [3]

Answer 5

energy is taken in / required to break bonds [1]
energy is given out when bonds are made [1]
the energy given out is greater than the energy taken in [1]